Method and means for heat exchanger control



Jan. 16, 1968 c. D. HALL ETAL 3,353,570

METHOD AND MEANS FOR HEAT EXCHANGER CONTROL 2 Sheets-Sheet 1 Filed March17, 1965 INVENTORS KI'TORNEYS CHESTER D. HALL MILL/1RD L. BROWN GARRETT7'. THURMAN R/CHARD A. K/NZ fi' Jan. 16, 1968 c. D. HALL ETAL METHOD ANDMEANS FOR HEAT EXCHANGER CONTROL 2 Shets-Sheet 2 Filed March 17, 1965INVENTORS CHESTER Dv HALL MILL/4R0 L. BROWN GARRETT 7'. THURMAN RICHARDA. Kl/VZ FIGS TORNEYS United States Patent 3,363,670 METHOD AND MEANSFOR HEAT EXCHANGER CONTROL Chester D. Hall, Millard L. Brown, Garrett T.Thurman,

and Richard A. Kinz, El Paso, Tex., assignors to Chevron ResearchCompany, a corporation of Delaware Filed Mar. 17, 1965, Ser. No. 440,4814 Claims. (Cl. 165-1) This invention relates to shell-and-tube heatexchangers, and more particularly to shell-and-tube heat exchangersarranged to reduce thermal stress within their shell sections. Stillmore particularly, it relates to internal bypass valving systems tocontrol the quantity of tube-side fluid passing through such exchangers.

In this application, the term shell-and-tube heat exchanger refers to anexchanger having, among other things, (1) a tube bundle for conveying atube-side fluid in at least two passes through the exchanger; (2) asheli section for supporting the tube bundle and conveying shell-sidefluid in at least a single pass through the exchanger in heat transfercontact with the tube-side fluid: (3) a channel section attached at oneend of the shell section to provide separate inlet and outlet chambersfor the tube-side fluid-these chambers preferably being provided bymeans of a baffle longitudinally disposed Within the section; and (4) anarrangement for reducing the thermal stresses between the tube bundleand the shell during operation of the exchanger. The last-mentionedarrangement typically includes a floating header section attached to theshell at an end opposite the channel section to allow differentialexpansion of the tube bundle relative to the shell and also to providefor reversal of the tube-side fluid. However, it is intended that otherstress-relieving arrangements may be used in conjunction with thisinvention; for example, by disposing a U-tube bundle Within the shell.

-It is a particular object of this invention to provide a rugged andinexpensive bypass system for a shell-andtube heat exchanger that willpermit internal control of tube-side fluid passing through theexchanger, but such control to occur without a corresponding increase intube-side system pressure. In carrying out this object, the exchanger inaccordance with the invention is constructed with an internal valvesystem for connecting tube-side fluid directly across the channel baffleof the exchanger. By such an arrangement, the tube-side fluid passesdirectly from the inlet to the outlet chamber of the exchanger withoutfirst passing through the shell section. In a preferred form of theapparatus, this valve system includes a valve stem entering the channelsection through one of the channel nozzles, one end of stem preferablyconnect ing to a valve plug in contact with a valve seat or sleevewelded to the channel baflle. The sleeve extends through an aperture inthe channel baflle and includes vertical slots extending parallel to theaxis of the stem; the slots increase in height as the plug and stemundergo vertical movement to adjust the fluid contact between the inletand outlet chambers. The capacity of the valve system may be varied, forexample, as a function of the exhaust temperature of the shell-sidefluid to reduce the heat transfer efliciency of the exchanger andprovide a desired temperature level within the exchanger withoutincreasing the system pressure or adding expensive piping and valves tothe exchanger. Furthermore, the system may be. incorporated withinexisting exchangers with minimum ex-.

penditures of time and material. Additionally, the variation in capacityprovided by the valve may be co-ordinated with the amount of fluidexternally bypassed around the exchanger to increase the control rangeof the external system.

3,363,670 Patented Jan. 16, 1968 Other objects and advantages of theinvention will become more apparent from the following detaileddescription, in which:

FIGURE 1 is a schematic diagram of a shell-and-tube heat exchangerincorporating the invention;

FIGURE 2 is a sectional view taken across line 22 of FIGURE 1illustrating in internal bypass valving system;

FIGURE 3 is an elevational view taken along line 33 of FIGURE 2;

FIGURE 4 is a side View taken along line 44 of FIGURE 2;

FIGURE 5 is an enlarged detail of the internal bypass system of FIGURE2; and

FIGURE 6 is a sectional view taken along line 6-6 of FIGURE 5.

Referring now to the drawings, particularly FIGURE 1, shell-and-tubeheat exchanger 10, constructed in accordance with the invention,transfers thermal energy between adjacently circulating fluids withinthe exchanger; i.e., between shell-side fluid 11 entering the exchangerat inlet shell nozzle 12 and tube-side fluid 13 entering the outletexchanger nozzle at inlet channel nozzle 14. In conventional manner, theshell-side fluid may be baflled to undergo a sinuous path through theshell section 15 and exits, after a single pass through the shell, atoutlet shell nozzle 16. The tube-side fluid is conveyed throughshellside section in at least two passes by a multiplicity of tubes 17known as a bundle (see FIGURE 2). In more detail, the tube-side fluid:

Enters the exchanger at channel section 18,

Passes through the tube bundle 17 to header section 19,

Returns through the tube bundle to channel section 15,

and

Thereafter passes from the exchanger via outlet channel nozzle 20.

Pressure is applied to both fluids by pumping units, not shown.

As indicated in FIGURE 1, the exchanger 10 may be used in conjunctionwith an external bypass piping network 21 connected between the inletand outlet nozzles of the channel section. The purpose of the network isto carry a portion of tube-side fluid around the shell section to lowerthe heat transfer efliciency of the exchanger as changes occur inexternal process conditions. It is, of course, intended that the amountof tube-side fluid passing through the external network be varied, as byvalves, to provide desired temperature conditions within the exchanger.However, if a change in operative conditions occurs in the tube-sidefluid system, for example, there may be corresponding increases in theefliciency of the heat exchanger that cannot be nullified by the bypassnetwork. As the exchanger overheats, or alternatively undercoolsdepending on the function of the tube-side fluid vis-a-vis theshell-side fluid, the effect may be to render the exiting shell-sidefluid in compatible with the process external of the exchanger.

Since a change in operating condition usually occurs after the heatexchanger is designed and functioning within a given process, it isimportant that the modification to the exchanger to increase bypasscapacity be accomplished in minimum time and, furthermore, provide verylittle change in over-all tube-side system pressure. Additionally, sincethe external piping network .is relatively expensive to modify, it isalso important tem 30 includes a valve seat or sleeve 31 open at itsends to connect inlet chamber 32 of the channel section with outletchamber 33 to increase the quantity of tube-side fluid bypassing theshell section 15. As indicated, sleeve 31 is anchored at its upper endto chamber baflie 34 and extends downward, as viewed, through aperture35 in the baffle into the lower chamber 33.

Contact between the sleeve and channel baffle occurs only at the upperend of the sleeve. In operation of the exchanger, the sleeve istherefore free to expand relative to the baffle to reduce the occurrenceof stress concentration along its length. Inasmuch as the sleeve isclosed at its lower end, slots 36 are provided in the side wall topermit fluid communication of the chambers. These slots arecircumferentially separated by ribs 37 for suflicient width to withstandsytem pressure as the tube-side fluid is bypassed through the sleeve.

The diameter of the sleeve and the width and height of the slots shouldbe large enough to reduce the capacity of the tube-side fluid passingthrough the exchanger to an effective level. That is, the amount oftube-side fluid passing through the valve system 30 must be to asufficient level to reduce the heat transfer efiiciency of the exchangerwhereby to provide the shell-side fluid with a desired exhausttemperature.

Flexibility in controlling the flow rate of the tube-side fluid throughthe sleeve 31 is provided by plug 38. In this embodiment, the plug ispreferably frustoconically shaped to facilitate its movement through thesleeve and includes a lower edge 40 (FIGURE in contact with the sidewall of the sleeve. An arcuate central surface 41 extends upward andaway from the edge; its purpose is to deflect the tube-side fluidthrough the slots with minimum turbulence. Contact between the plug andsleeve occurs only in one planein the intersection of edge 40 with theribs 37. Movement of :the plug relative to the sleeve to provide acorresponding change in slot height 39 is therefore relatively easy toachieve.

In this embodiment, control of plug 38 is provided by the verticalmovement of stem 42, to which the plug is attached; but other valve andcontrol arrangements can be used if desired. A requirement in suchsystems, however, is that the stem 42 or other control means for thevalve pass into the exchanger through the channel nozzles to minimizestress concentrations within the shell. The lower end of the stem 42 issecured to the plug by a reducer 44 attached to the stem by welding. Thereducer also includes threads at its lower exterior for attachment tothe plug. The plug is keyed to the reducer by safety wire 45. Whenrepairs are necessary, this arrangement makes for easy replacement ofdamaged parts.

The upper end of the stem is attached to chain wheel 56 at the exteriorof the exchanger by which an operator can adjust the slot height of thesleeve. In this arrangement, pressure integrity is maintained by passingthe stem from the exchanger through a pressure-tight bonnet 51 attachedto a flanged support 52 above the channel nozzle 14. Flanged inletpiping 53 is attached to the channel nozzle below support 52 but ispreferably arranged to form a Y-junction with the support to allow thealignment of the stem 42 within both the bonnet 51 and the sleeve 31.Although the axes of the support 52, channel nozzle 14, and the sleeve31 are illustrated as collinear for this purpose, the stem could beconstructed with flexible joints along its length to compensate fordeviations in alignment.

Pressure-seal bonnet 51 includes a flanged base 55 attached to support52. Above the base is attached a yoke 56 (see FIGURE 4) terminating inthreaded hub 57 through which the stem 42 threadably engages. Bolts 58attach to bonnet 59 and apply pressure of stuffing box 60 to preventflow of fluid from the interior of the eX- changer.

Rotation of the stem from a level below chain wheel 50 is provided byendless chain 61 riding over rollers 62,

through guides 63, and thence around the chain wheel (see FIGURE 3).Guides 63 are stationarily fixed in space by means of yoke 64 rotatablyattached to the stem. As indicated in FIGURE 4, rollers 62 are attachedto a central shaft 65 journaled at its ends to frame 68. The lower partof the frame 68, in turn, is attached to the flange of pipe 53 and tothe base of bonnet 51 as indicated.

The relative height of the plug above the end wall of the sleeve willvary depending upon the operating conditions of the exchanger. Ingeneral, it will be in the order of l to 5 inches long to provideflexibility in adjusting varying exchanger operating conditions.

Correct spacing of the plug relative to the end wall of the sleeve maybe preferably determined under process operating conditions. Initiallythe plug is preferably positioned in a plane intersecting the chamberbatfle 34; but, after the exchanger has been put on-streazm, the stemand plug undergo downward movement, as viewed, to increase flow of thetube-side fluid through the internal valving system. As viewed in thefigures, as the plug clears the upper end of the slots, tube-side fluidpasses downward through the sleeve and then is deflected in radialdirections by the arcuate central surface of the plug through the slots36 into the lower chamber 33 and thence removed from the exchanger byoutlet nozzle 20. As the amount of tube-side fluid increases in fixedincrements occurring, say every five minutes, the exhaust temperature ofthe shell-side fluid is monitored. When the desired operating exhausttemperature is achieved, movement of the stem is terminated, positivelocking of the stem occurring by virtue of screwable connection betweenthe stem and hub 57 of the bonnet 51 exterior of the exchanger.

Utilization of existing structure of an exchanger to provide bypasscontrol of the tube-size fluid (where modiflcation of an existingexchanger is necessary) is a further advantage of the present invention.For example, aperture 35 may be provided in the baflie 34 without thenecessity of the baffle being removed from the exchanger. Likewise,other parts of the system are similarly attached to the exchanger withminimum expenditure of time and money.

Further flexibility of the exchanger internal bypass system may beachieved by using control features of the external bypass network 21. Toprovide a maximum control capacity through the external bypass network,the adjustments in the internal valve previously described arepreferably undertaken after the capacity of the external bypass systemhas been reduced as to say one-half capacity. Consequently, after adesired plugsleeve setting for the internal valve is achieved, theexternal piping network will provide maximum flexibility in adjustingthe rate of flow of tube-side fluid through the exchanger, as changes inoperating conditions occur.

In many applications, automatic response of the internal valving systemto changes in process conditions may also be desirable. On an automaticsystem compatible with existing exchangers, a temperature-sensitivetransducer may be arranged to be supported in shell exhaust nozzle 16.The transducer has bimetal elements whose movements reflect any changesin temperature of the shell-side fluid. The bimetal elements aredesigned to close a relay as the temperature increases that in turntrips a motor through a timing circuit. The motor drives the valvecontrollers, as for example stem 42 in rotation causing verticalmovement of the controller relative to the valve seat. The purpose ofthe timing circuit is to prevent the controller from being overdrivenduring adjustment of valve aperture. A delay interval of five minutesbetween relay and motor actuation is sufficient for this purpose. It isto be noted that the system may be further modified to vary thedirection of the rotation of the controller, either clockwise orcounterclockwise, as a function of the sign of the transducer signal toadd further flexibility to the system.

Various changes in the structure shown and described will occur to thoseskilled in the art. All such changes are intended to be included withinthe scope of the intended claims.

We claim:

1. In a heat exchanger control system including a shelland tube-heatexchanger having a shell section for conveying shell-side fluid throughsaid exchanger, a tube bundle within said shell section for conveyingtube-side fluid through said exchanger in heat transfer contact withsaid shell-side fluid, an inlet-outlet channel section for saidtube-side fluid in operative contact with said tube bundle, a channelbaflie separating said channel section into an input chamber and anoutput chamber, each of said chambers in fluid contact with one end ofsaid tube bundle, and an external bypass piping network connected tosaid exchanger for externally bypassing a portion of said tube'sidefluid about said exchanger so as to control the efliciency of heattransfer Within a predetermined range within said heat exchanger, theimprovernent comprising an internal bypass valve system for saidtube-side fluid within said channel section adapted to extend the rangeover which said heat transfer is controlled, said internal bypass valvesystem including (a) a sleeve means attached to and extending throughsaid channel bafiie, said means having an aperture therein to place saidtwo chambers in fluid communication, and y (b) control means operativelyconnected to said sleeve means for varying the rate of flow of saidtube-side fluid between said chambers and thereby extend saidpredetermined control range of said system.

2. The combination of claim 1 in which said control means includesactuating means adapted to initiate operation of said control means fromthe exterior of said exchanger.

3. The combination of claim 1 wherein said control means includes avalve plug operatively connected and seated within said sleeve means, avalve stem connected at one end to said valve plug and extendingexterior of said exchanger for moving said stem relative to said sleeve;and pressure seal means exterior of said exchanger operatively connectedto said stem and attached to a portion of said exchanger.

4. A method of extending the range of a heat exchanger control systemwhich includes a heat exchanger adapted to pass tube-side fluid from aninput-output channel section having a longitudinal channel baifletherein to divide said channel section into first and second chambers,to a multiplicity of tubes within a shell section attached to saidchannel section so as to place the tube-side fluid in heat transfercontact wtih a shell-side fluid passing through the shell sectionexterior of the multiplicity of tubes, and an external bypass pipingnetwork connected to said exchanger, comprising the steps of:

(a) forming an aperture in said channel bame in said channel section toplace said first and second chambers in direct fluid contact;

(b) arranging a normally closed valve means in operative contact withinsaid aperture;

(c) flowing the tube-side fluid and shell-side fluid in heat transfercontact through said exchanger;

(d) simultaneous with step (c) flowing tube-side fluid in the externalpiping network about said exchanger at full capacity so that a portionof said tube-side fluid bypasses the exchanger to control the efiiciencyof heat transfer between the fluids within the exchanger within apredetermined range;

(e) incrementally opening said valve means in said channel section topass a portion of tube-side fluid through said aperture so as to extendthe heat transfer control range of the system, and

(f) terminating said increase in flow of said tube-side fluid when theefliciency of heat transfer between the fluids in the exchanger reachesa desired level.

References Cited FOREIGN PATENTS 859,746 12/1952 Germany. 351,138 6/1931Great Britain. 766,614 1/1957 Great Britain.

ROBERT A. OLEARY, Primary Examiner. C. SUKALO, Assistant Examiner.

1. IN A HEAT EXCHANGER CONTROL SYSTEM INCLUDING A SHELL- AND TUBE-HEATEXCHANGER HAVING A SHELL SECTION FOR CONVEYING SHELL-SIDE FLUID THROUGHSAID EXCHANGER, A TUBE BUNDLE WITHIN SAID SHELL SECTION FOR CONVEYINGTUBE-SIDE FLUID THROUGH SAID EXCHANGER IN HEAT TRANSFER CONTACT WITHSAID SHELL-SIDE FLUID, AN INLET-OUTLET CHANNEL SECTION FOR SAIDTUBE-SIDE FLUID IN OPERATIVE CONTACT WITH SAID TUBE BUNDLE, A CHANNELBAFFLE SEPARATING SAID CHANNEL SECTION INTO AN INPUT CHAMBER AND ANOUTPUT CHAMBER, EACH OF SAID CHAMBERS IN FLUID CONTACT WITH ONE END OFSAID TUBE BUNDLE, AND AN EXTERNAL BYPASS PIPING NETWORK CONNECTED TOSAID EXCHANGER FOR EXTERNALLY BYPASSING A PORTION OF SAID TUBE-SIDEFLUID ABOUT SAID EXCHANGER SO AS TO CONTROL THE EFFICIENCY OF HEATTRANSFER WITHIN A PREDETERMINED RANGE WITHIN SAID HEAT EXCHANGER, THEIMPROVEMENT COMPRISING AN INTERNAL BYPASS VALVE SYSTEM FOR SAIDTUBE-SIDE FLUID WITHIN SAID CHANNEL SECTION ADAPTED TO EXTEND THE RANGEOVER WHICH SAID HEAT TRANSFER IS CONTROLLED, SAID INTERNAL BYPASS VALVESYSTEM INCLUDING (A) A SLEEVE MEANS ATTACHED TO AND EXTENDING THROUGHSAID CHANNEL BAFFLE, SAID MEANS HAVING AN APERTURE THEREIN TO PLACE SAIDTWO CHAMBERS IN FLUID COMMUNICATION, AND